The first phase of the campaign, which is expected to last almost four weeks, will immunize at least 650,000 people [File; Paula Bronstein/Getty Images]

Many of the Rohingya refugees are children and have arrived without their parents [File: Cathal McNaughton/Reuters]

Bangladeshi government, UN agencies, and a number of NGOs have launched a massive vaccination campaign in Bangladeshâs CoxâS Bazar to save hundreds of thousands of Rohingya refugees from the spread of cholera outbreak.

Bangladesh's Ministry of Health, supported by The World Health Organisation (WHO), UNICEF and other NGOs distributed oral vaccine to 88,000 Rohingya on Tuesday in a large-scale camp aign that aims to vaccinate 650,000 people in the next three and a half weeks.

It's the second-largest oral vaccination campaign in the world, after another in Haiti last year. It will involve 900,000 doses of vaccine.

A second phase of immunisations, which is expected to begin November, aims to immunise 250,000 children between the age of one and five.

Although no cases of cholera have been officially recorded, the vaccination campaign is a precautionary measure to prevent a full-on breakout.

However, at least 10,292 cases of diarrhea, which are symptomatic to cholera, have been diagnosed by WHO so far.

"I won't be surprised if we have a few cholera cases coming among all these diarrheal diseases because it is inevitable," Dr. Navaratnasamy Paranietharan, a WHO representative at Cox's Bazar, told Al Jazeera.

"With the vaccination campaign and based on our analysis, we do not expect a large cholera out break among this population. It's not going to be like Yemen or other places."

Paranietharan said the WHO will have lab results as soon as next week, which will likely confirm cholera's presence in the refugee camps.

The conditions in the camp are alarming: It's wet, muddy and overcrowded. There is also a shortage of clean water and sanitation.

"There are very few toilets here," said Gura Banu, Rohingya refugee in Cox Bazar. "In a period of three to five days, it becomes full and unusable. It stinks a lot. There are too many people here. We can live without eating once or twice a day but we can't live without being able to use the toilets."

Most of the refugees are living on one meal a day and torrential rains, followed by relentless heat waves, have further complicated their conditions.

"The water is too far away," said Muhamad Shaker, another Rohingya. "That's a problem and pe ople are suffering. There are just too many people here and that's why it's so dirty. Everyone is getting sick."

The United Nations High Commissioner for Refugees (UNHCR) has urged for precautionary measures to avoid the outbreak.

"Clean water and safe drinking water is critical in reducing and preventing these kind of diseases," Yante Ismail, a UNHCR spokesperson, told Al Jazeera.

Leonard Doyle, spokesperson for the International Organization for Migration echoed the warning.

"A seven-year-old boy came up to me and he put his hand across his throat to indicate that his father had died, been killed and slaughtered and he himself had just [arrived] the night before. So that gives you the sense of how horrible the whole situation is."

Cholera kills 95,000 p eople each year and affects an additional 2.9 million people worldwide. It's an acute diarrheal infection caused by ingesting contaminated food or water that causes mild symptoms including dehydration and diarrhea.

The disease often strikes regions steeped in conflict that have a lack of sanitation and where malnutrition runs rampant. Cholera can be fatal within hours if untreated.

"Dehydration can take hold very quickly and that's the risk," Nichola Jones, a spokesperson for the International Federation of Red Cross and Red Crescent Societies, told Al Jazeera.

"Children are especially vulnerable. We're seeing the arrival in recent days of people who've been travelling for even longer than many of the others who arrived in the last month. Some people say they left Rakhine up to two weeks ago. They're already exhausted and dehydrated and we are extremely concerned about the health of these people in particular."

The vaccination campaign is a step in the right direction, but Al Jazeera's Mohammed Jamjoom, who's currently reporting the situation from Cox's Bazar, stressed Bangladesh security forces and NGOs are facing mounting difficulties.

"The conditions are appalling in these camps, they're extremely unhygienic," he said.

"They're worried that this could erupt into a full-blown health crisis. This is going to be a massive undertaking because, these for the most part, aren't formal, well-organized settlements, they are makeshift camps and it's hard to find people in them, it's hard to organise things in them, it's hard to ensure that aid is flowing, that people can get to the areas where they can get vaccine and water and other supplies."

Al Jazeera correspondent said that many Rohingya are relieved an immunisation campaign is underway, but emphasised more needs to be done to counter a full-scale epidemic.

"Many of them said that there are few toilets in the camp, that if a new one is built than people can use if for three days then it's unusable after that. They're saying that it's just too overcrowded, they're saying that it's too difficult to get water, they need more clean water."

More than half a million Rohingya have fled ethnic violence in Myanmar's Rakhine State in the past six weeks, and roughly 2,000 continue to trickle across the border everyday.